This invention relates to heavy duty pneumatic tires such as are commonly used on earthmoving equipment, aircraft, agriculture and specialty applications such as run-flat tires, and more particularly to pneumatic tires having a specified relationship between the lower bead area of the tire and a flange portion of an associated rim upon which the tire is designed to be mounted.
Pneumatic tires that experience high loads and deflections such as off-the-road earthmover and airplane pneumatic tires have historically been subjected to tremendous stresses and heat buildup problems in the bead area. Agricultural drive axle tires and specialty tires similarly experience extremely high levels of torque which requires the bead and rim fitmer to be precisely matched to avoid tire-to-rim slippage. These tires operate at very high internal pressures and are filled with large volumes of internal fluids, generally air or some other inert gas. Radial deflections of these tires generally occur under very high impacts while the tire is heavily loaded. In the past, these tires would deflect with the bead portion contacting the rim flange harshly. Repeated impacts in this area can cause a phenomena commonly referred as xe2x80x9cbead erosionxe2x80x9d. These severe deflections stress the internal components of the tire carcass such as ply endings and other component interfaces, and if severe enough can initiate ply ending separation or other associated problems which can injure the tire""s casing.
A recent development in pneumatic tires is the run-flat passenger tire. These run-flat tires, unlike the abovementioned high pressure and high-torque tires of the aircraft and off-the-road industry, normally operate similarly to conventional passenger tires with one big exception, these tires generally have stiffened sidewalls that when the tire is operated with little or no air must support the weight of the vehicle. In such situations, high deflection and loads are transmitted to the bead area of the tire. Rapidly, these uninflated tires build up high heats which can limit the run-flat capability of the tire. In these circumstances, the run-flat passenger tire becomes overstressed and overloaded similar to the conditions seen in the high pressure, high load and high torque applications of the larger aircraft and off-the-road tires. Therefore, the run-flat tire design also must be equipped to accommodate these conditions.
In U.S. patent 5,368,082 a unique bead design was disclosed for run-flat tire applications. The bead was made of a single steel monofilament having a truncated triangular shape. This bead design had a very wide based that ensured that the tire remained seated on the rim when the tire was operated in an uninflated condition. The tire had a hard rubber apex flange. The bead core was radially extended a distance substantially below the radially outer surface of the rim flange.
Large pneumatic tires to be used on earthmoving equipment, commonly known as earthmover tires, are well known. Earthmover tires are required to perform in difficult environments. When used xe2x80x9coff-the-roadxe2x80x9d, they are required to provide excellent traction for extremely heavy vehicles pushing, pulling and lifting extremely heavy loads. The environment is fraught with rocks and other sharp debris which can damage the tires. Due to the relatively high cost of these large tires, durability and long life is a primary design parameter. A second environment in which the tires might be expected to perform is on public highways. Sometime the earthmoving equipment must travel on such highways to move from construction site to construction site.
Previously, the required strength was built into such tires by incorporating certain curves into the molded shape of the exterior of the tire. These extra curves or bulges were believed to give extra support to those areas of the tire where durability was especially important, such as the lower sidewall, mid sidewall and tread center. In the bead flange area, the prior art off-the-road tires employed an interference fit whereby the tire bead portion was in contact with the radially outer surface of the rim flange. Off-the-road tire engineering conventionally added mass to structurally improve the durability of the tire.
In the aircraft tire art, tire engineers must look to reduce mass due to the unique weight limitations. Still the tires still must be durable.
In U.S. Pat. Nos. 4,790,364 and 4,813,467 an aircraft tire and rim combination is disclosed which shows a clearance between a rim flange and the surface of the bead portion of the tire. Although aircraft tires are much different in construction and design compared to earthmover tires or off-the-road tires, they still must survive these high deflections and overload conditions previously discussed.
In U.S. Pat. No. 5,429,168 a unique earthmover design was developed that had permitted a reduction in the thickness of the lower sidewall region and bead portions of the tire by providing a clearance between the rim flange and the bead portion. That invention was particularly adapted for a radial ply carcass construction. It achieved in an earthmover tire some of the beneficial attributes of the aircraft tire technology.
In the present invention a unique bead core design has been found to be very beneficial in both bias or radial ply heavy duty tire applications. As used herein heavy duty tire applications include off-the-road, earthmover, aircraft, agricultural tires and specialty industrial type tires as well as the new run-flat tire technology. The unique design of this bead core enables large reductions in rubber mass to be achieved while increasing the lateral stiffness of the bead portion of the tire.
The present invention also has as one of its objects improved durability in the heavy duty tires, but does so by providing a bead area design which has demonstrated a marked improvement over the prior art.
It is therefore, an object of the invention to provide a heavy duty tire having improved durability.
It is another object of the invention to provide a heavy duty tire having a bead portion which cooperates with the flange portion of an associated rim to improve the durability and rigidity of the bead portion of the tire.
It is a further object of the invention to provide a heavy duty tire bead core having a certain relationship between the flange area of the tire in the rim flange, such relationship creating a clearance between the tire and the radially outer surface of the rim flange. The nature of the clearance is discussed herein and meets certain requirements in order to provide the durability sought.
An improved heavy duty pneumatic tire 11 is disclosed. The improved heavy duty pneumatic tire 11 has a nominal rim diameter D, an axis of rotation and a carcass 14 having a pair of bead portions 25. Each bead portion 25 has at least one annular inextensible bead core 15. The carcass 14 for a radial ply tire further includes a cord reinforced radial ply 18 extending between and wrapped around the bead core 15. The carcass 14 for a bias ply tire 110 includes pluralities of cord reinforced pairs of bias plies 180. The bias plies 180 have turnup ends 280 that wrap about one or more bead cores 15,150,151,250,251,252. The tire 11,110 has ply turnup ends 28,280 extending axially and radially outwardly from each bead core 15,150,151,250,251,252 and the plurality of reinforcing belt disposed radially outwardly of the ply or plies. A tread 12 is disposed radially outwardly of the carcass 14. Each bead portion has a radially inner first surface 96 and a radially outwardly extending second surface 100. The first and second surfaces 96, 100 of the bead portion 25 are designed to engage a design rim as specified by the applicable standards organization. The design rim 60 has a pair of bead seat portions 92 and a pair of rim flange portions 98 respectively. Each bead portion has the first surface 96 contacting the bead seat portion 92 of the rim 60 and the radially outwardly extending second surface 100 contacting a radially inner portion of the rim flange portion 98. When the tire 11 is mounted onto the rim 60, uninflated and unloaded, the second surface 100 and the rim flange 98 initially cease contact diverge from each other at a location 101 in the cross section of the tire and rim in the region of the flange. One or more bead cores 15,150,151,250,251,252 in each bead portion 25 extend radially outwardly beyond the radial height (H) of the rim flange radially outer surface 100.
The bead cores 15 extend above the rim flange 98 preferably having a radially outer portion 15A that is triangularly shaped and a radially inner portion 15B that rectangular, square, round or trapezoidal in shape. Most preferably the bead core 15 is made of a single monofilament steel or high tensile steel wire wrapped successively to achieve the desired shape.
Definitions. xe2x80x9cAspect ratioxe2x80x9d of the tire means the ratio of its section height (SH) to its section width (SW);
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means lines or directions that are parallel to the axis of rotation of the tire;
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim;
xe2x80x9cBelt reinforcing structurexe2x80x9d means at least two layers of plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17 degrees to 27 degrees with respect to the equatorial plane of the tire;
xe2x80x9cBias Ply Tirexe2x80x9d means that the reinforcing cords in the carcass ply extend diagonally across the tire from bead-to-bead at about a 25-50xc2x0 angle with respect to the equatorial plane of the tire, the ply cords running at opposite angles in alternate layers;
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, under tread, and sidewall rubber over the plies, but including the beads;
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction;
xe2x80x9cChafersxe2x80x9d refers to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim, and to seal the tire;
xe2x80x9cChippersxe2x80x9d means a reinforcement structure located in the bead portion of the tire;
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands of which the plies in the tire are comprised;
xe2x80x9cDesign rimxe2x80x9d means a rim having a specified configuration and width. For the purposes of this specification, the design rim and design rim width are as specified by the industry standards in effect in the location in which the tire is made. For example, in the United States, the design rims are as specified by the Tire and Rim Association. In Europe, the rims are as specified in the European Tyre and Rim Technical Organizationxe2x80x94Standards Manual and the term design rim means the same as the standard measurement rims. In Japan, the standard organization is The Japan Automobile Tire Manufacturer""s Association.
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread;
xe2x80x9cInnerlinerxe2x80x9d means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire;
xe2x80x9cNormal rim diameterxe2x80x9d means the average diameter of the rim flange at the location where the bead portion of the tire seats;
xe2x80x9cNormal inflation pressurexe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire;
xe2x80x9cNormal loadxe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire;
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords;
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d means directions radially toward or away from the axis of rotation of the tire;
xe2x80x9cRadial-ply tirexe2x80x9d means belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from the bead to bead are laid at cord angles between 65 degrees and 90 degrees with respect to the equatorial plane of the tire;
xe2x80x9cSection heightxe2x80x9d (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane; and,
xe2x80x9cSection widthxe2x80x9d (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.